Determinants of the decline in mortality attributable

Transcription

1 Temporal Trends in the Incidence of Coronary Disease Theresa J. Arciero, Steven J. Jacobsen, MD, PhD, Guy S. Reeder, MD, Robert L. Frye, MD, Susan A. Weston, MS, Jill M. Killian, BS, Véronique L. Roger, MD, MPH PURPOSE: Mortality due to coronary disease has declined, but the incidence of myocardial infarction has changed little. Whether the incidence of myocardial infarction reflects that of overall coronary disease is unknown. This study was designed to determine whether the incidence of coronary disease has declined over time. METHODS: We ascertained incident cases of overt coronary disease (myocardial infarction, sudden death, angiographically diagnosed coronary disease, unstable angina not identified under other rubrics) between 1979 and 1998, using medical records of patients in Olmsted County, Minnesota. Secular trends were analyzed with Poisson regression. RESULTS: Between 1979 and 1998, there were 5772 incident cases of coronary disease (myocardial infarction: 1991; sudden death: 1056; angiographically diagnosed coronary disease: 2514; unstable angina: 211). The age- and sex-adjusted incidence of myocardial infarction declined 6% during these two decades and 3% in the second decade, whereas the incidence of myocardial infarction and sudden death combined declined 17% in the first two decades and 9% in the second decade. Use of angiography increased and served as a measure of coronary disease incidence in the second decade. During the second decade, trends in the incidence of all coronary diseases paralleled those of myocardial infarction and of myocardial infarction and sudden death combined, declining 9% (P 0.06). Cases of coronary disease diagnosed angiographically increased during the period studied. CONCLUSION: The trends that we observed suggest that myocardial infarction and sudden death constitute suitable indicators of trends in coronary disease. The decline in incident coronary disease cases supports the hypothesis that the decline in mortality is explained in part by primary prevention and secondary prevention partially mediated by earlier detection. Am J Med. 2004;117: by Elsevier Inc. From the Divisions of Epidemiology (SJJ), Cardiovascular Diseases and Internal Medicine (GSR, RLF, VLR), and Biostatistics (SAW, JMK), Mayo Clinic, and Mayo Medical School (TJA), Mayo Clinic College of Medicine, Rochester, Minnesota. Supported in part by grants from the Public Health Service and the National Institutes of Health (AR30582 and R01 HL59205). Dr. Roger is an Established Investigator of the American Heart Association. Requests for reprints should be addressed to Véronique L. Roger, MD, Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905, or roger.veronique@mayo.edu. Manuscript submitted August 6, 2003, and accepted in revised form March 1, Determinants of the decline in mortality attributable to coronary disease have not been fully elucidated. Recent data indicate little change in the incidence of myocardial infarction in contrast with declines in mortality due to coronary disease (1,2). Secondary prevention may have contributed to the decline in mortality, although data from the Monitoring Cardiovascular Disease study indicated that changes in coronary disease rates were responsible for reduced mortality, thus pointing to primary prevention as a key factor (3,4). Most studies used myocardial infarction and sudden death as the chief indicators of the incidence of coronary disease, but few included persons older than 74 years, the fastest growing segment of the population (1 4). Other potential indicators of coronary disease are angina pectoris (chronic or unstable) and angiographically diagnosed coronary disease. Angiography documents coronary disease using criteria that have remained constant since its practice implementation. Patterns in its use can be quantified to interpret trends in coronary disease incidence. Unstable angina is a better marker than chronic angina for surveillance of coronary disease, correlating with more severe symptoms and often leading to the use of tests with standardized and quantifiable results. The Rochester Epidemiology Project (5) is uniquely positioned to use surveillance methods to gain insight into the incidence of coronary disease. Thus, this study was undertaken to examine the trends in the incidence of measurable manifestations of coronary disease, namely, myocardial infarction, sudden death, angiographically diagnosed coronary disease, and unstable angina not otherwise identified, and to determine whether the incidence of coronary disease has declined over time. METHODS The study was conducted in Olmsted County, Minnesota (6). The county comprises a predominantly white population and is relatively isolated from other urban centers. Mayo Clinic and Olmsted Medical Center provide nearly all medical care for the local population. These institutions have accumulated comprehensive records that contain high-quality information from all health care encounters, including laboratory results, pathology reports, and autopsy results. The Rochester Epidemiology Project maintains extensive indexes based on clinical and histo by Elsevier Inc /04/$ see front matter All rights reserved. doi: /j.amjmed

2 logic diagnoses and surgical procedures for all providers of care to county residents, and all records are linked from all sources of care for this population. The study was approved by the Mayo Foundation Institutional Review Board. Data Collection Events selected to define coronary disease were myocardial infarction, sudden death, angiographically diagnosed coronary disease, and unstable angina not otherwise identified under the other rubrics. Myocardial infarction. The methods used to ascertain the incidence of myocardial infarction relied on epidemiological criteria (7,8). Briefly, cases with diagnoses compatible with myocardial infarction were identified from the Rochester Epidemiology Project indexes, reviewed by trained abstractors, and validated using data on cardiac pain, elevated biomarker values, and electrocardiography (7,9). Sudden death. The methods used to ascertain sudden death due to coronary disease relied on validated criteria based on death certificate data (8). Deaths were classified as sudden if they occurred out of the hospital and were assigned codes 410, 411, 412, 413, or 414 of the International Classification of Diseases, Ninth Revision (ICD-9) (10). Angiographically diagnosed coronary disease. The Mayo Clinic Catheterization Laboratory maintains a computerized registry of all coronary angiography procedures, allowing identification of all procedures performed on county residents. Severe disease was defined angiographically as stenosis involving more than 75% of the left anterior descending, left circumflex, or right coronary artery, or 50% of the left main coronary artery (11). To provide a more comprehensive measure of the coronary disease burden, it is important to consider other indicators such as angiographically diagnosed coronary disease. The trends in angiographically diagnosed coronary disease should be interpreted within the context of the trend in use of coronary angiography, which increased considerably between 1979 and 1988 (181%), stabilizing thereafter, with an increase of 13% between 1988 and Thus, angiographically diagnosed coronary disease was included with myocardial infarction, sudden death, and unstable angina not already identified under the other rubrics as a measure of any coronary disease from 1988 to Unstable angina. Cases of unstable angina (defined by code 411, other acute and subacute forms of ischemic heart disease) were included if they were not identified among the previous three diagnostic rubrics. Ascertaining Incident Events We used three definitions to categorize incident coronary disease events, each gradually broader in scope: myocardial infarction; myocardial infarction and sudden death combined; and a combination of myocardial infarction, sudden death, angiographically diagnosed coronary disease, and unstable angina (referred to hereinafter as any coronary disease ). The incident nature of the myocardial infarction was ascertained through manual review of the community records. Other events were defined as incident if not preceded by ICD-9 codes 410 and 411. For cases with more than one event on the same day, record review established timing. The completeness of the angiography database was assessed by comparing manually recorded procedures in the myocardial infarction incidence cohort (7) with those in the database. The comparison yielded concordance of 99%. To determine the reliability of using ICD-9 codes 410 and 411 to determine the incidence of sudden death and angiographically diagnosed coronary disease, electronic retrieval of codes 410 and 411 was compared with manual record review within the myocardial infarction incidence cohort to detect prior myocardial infarction cases. Relying solely on these two codes yielded a 4.8% underestimation of true incident myocardial infarction events, providing reassurance that this approach could be used to ascertain incident sudden death and angiographically diagnosed coronary disease, with the realization that the overestimation of true incident coronary disease events was less than 5%. Statistical Analyses Age-, sex-, and year-specific incidence rates for the three definitions of coronary disease events and summary rates were directly adjusted to the U.S. population distribution in The denominator for incidence rates was determined by Olmsted County population census data for 1970, 1980, and 1990, with linear interpolation for intercensal years. Standard errors and 95% confidence intervals were calculated using Poisson error distribution. Age- and sexspecific trends in the incidence of all manifestations of coronary disease were modeled using Poisson regression. The units of observation were age- and sex-specific counts, based on 10-year age groups using the midpoint of the age range for the regression model. The logarithm of the count was modeled with the logarithm of age- and sex-specific population size as the offset. Age and calendar year were analyzed as continuous variables. The results of the final model are presented as the relative risk of an incident manifestation of coronary disease in specific years compared with a baseline year in selected age groups for men and women. Trends across age groups and between sexes were compared by including the inter- August 15, 2004 THE AMERICAN JOURNAL OF MEDICINE Volume

3 action terms representing year and age, and year and sex. Analyses were performed using SAS software (SAS Institute, Inc, Cary, North Carolina); significance was set at P RESULTS In the two decades between 1979 and 1998, a total of 5772 persons had an initial manifestation of coronary disease (myocardial infarction: 1991; sudden death: 1056; angiographically diagnosed coronary disease: 2514; and unstable angina not otherwise identified: 211). The median age was 69 years; 35% (n 2013) of all patients were aged 75 years or older. Thirty-eight percent (n 2221) were women. Angiographically diagnosed coronary disease comprised the largest proportion (44% [2514/5772]) of all incident coronary disease cases. The proportion of each possible coronary disease manifestation changed over time (P 0.001). Between 1979 and 1983, myocardial infarction accounted for 42% of all initial coronary disease manifestations, sudden death for 23%, and the remaining events consisted mostly of angiographically diagnosed coronary disease. The proportion of patients presenting with myocardial infarction decreased thereafter, stabilizing in later years. The proportion of cases of sudden death decreased continuously over time, from 23% during the period to 17% during the period. By contrast, the proportion of incident cases of coronary disease identified angiographically increased from 27% in the earlier years to 52% in later years. Myocardial Infarction There were 195 cases of incident myocardial infarction per 100,000 persons in 1979 (95% confidence interval [CI]: 154 to 237 cases/100,000 persons) and 182 cases of incident myocardial infarction per 100,000 persons (95% CI: 150 to 214 cases/100,000 persons) in 1998 a decrease of 0.35% (relative risk [RR] 0.996; 95% CI: to 1.004) per year. The age- and sex-adjusted incidence of myocardial infarction remained stable with a nonsignificant 6% decline (RR 0.94; 95% CI: 0.82 to 1.07) during the two decades studied (P 0.33) and a 3% decline during the second decade (RR 0.97; 95% CI: 0.90 to 1.03) (Figure 1). Myocardial Infarction and Sudden Death When myocardial infarction and sudden death were combined, the overall age-adjusted incidence was 297 cases per 100,000 persons (95% CI: 245 to 348 cases/ 100,000 persons) in 1979 and 280 cases per 100,000 persons (95% CI: 241 to 319 cases/100,000 persons) in The age- and sex-adjusted incidence declined by 0.9% (RR 0.991; 95% CI: to 0.996) per year a 17% decline between 1979 and 1998 (RR 0.83; 95% CI: 0.75 Figure 1. Age-adjusted incidence rates (cases/100,000 persons), represented by the solid lines, for any coronary disease, myocardial infarction and sudden death, and myocardial infarction in Olmsted County, Minnesota. Any coronary disease, which includes myocardial infarction, sudden death, angiographically documented disease, and unstable angina, is presented for the last decade of stable rates of angiography. The rapid increase in the use of angiography between 1979 and 1988 may have shortened the delay of diagnosis and caused a transient increase in event rate early in the second decade. The dotted line represents a smooth line fit to the data using a spline routine. to 0.93; P 0.001) and a 9% decline in the last 10 years of the study (RR 0.91; 95% CI: 0.86 to 0.96) (Figure 1). Twenty-six percent of cases of sudden death and MI occurred during the winter, compared with 24% during the summer. Any Coronary Disease The age-adjusted incidence of any coronary disease was 571 cases per 100,000 persons (95% CI: 508 to 635 cases/ 100,000 persons) in 1988 and 503 cases per 100,000 persons (95% CI: 451 to 556 cases/100,000 persons) in The incidence of any coronary disease was markedly higher than that of MI and sudden death. During the second decade studied, the incidence of all coronary disease declined by 9% (RR comparing 1988 and ; 95% CI: 0.82 to 1.01; P 0.06) (Figure 1). Age- and Sex-Specific Trends Between 1988 and 1998, men and younger persons were more likely to present with angiographically diagnosed coronary disease as the initial manifestation of coronary disease than were women and older persons (P for men vs. women; P for younger vs. older persons) (Table). Over time, the proportion of women and older persons presenting with angiographically diagnosed disease increased (P 0.02 for women; P for older persons), although the proportion of cases presenting with acute events (myocardial infarction or sudden death) remained higher among women and older persons than among men and younger persons. Secular trends in the incidence of myocardial infarction, myocardial infarction and sudden death combined, 230 August 15, 2004 THE AMERICAN JOURNAL OF MEDICINE Volume 117

4 Table. Initial Manifestation of Coronary Disease (1988 to 1998), by Age and Sex* 1988 to to 1998 Age Group (years) Characteristic Number (%) Men (n 448) (n 300) (n 264) (n 150) (n 363) (n 278) (n 262) (n 158) Myocardial infarction 145 (32) 82 (27) 82 (31) 37 (25) 114 (31) 62 (22) 67 (26) 47 (30) Sudden death 28 (6) 25 (8) 40 (15) 60 (40) 26 (7) 31 (11) 34 (13) 58 (37) Angiographically 264 (59) 186 (62) 128 (48) 42 (28) 221 (61) 185 (67) 161 (61) 53 (34) diagnosed coronary disease Unstable angina 11 (2) 7 (2) 14 (5) 11 (7) 2 (1) Women (n 99) (n 153) (n 193) (n 270) (n 109) (n 129) (n 219) (n 247) Myocardial infarction 43 (43) 55 (36) 64 (33) 117 (43) 50 (46) 45 (35) 79 (36) 77 (31) Sudden death 4 (4) 17 (11) 26 (13) 105 (39) 4 (4) 9 (7) 27 (12) 105 (43) Angiographically 52 (53) 76 (50) 96 (50) 37 (14) 54 (50) 75 (58) 112 (51) 65 (26) diagnosed coronary disease Unstable angina 0 5 (3) 7 (4) 11 (4) 1 (1) 0 1 (1) 0 * Percentages within age groups may not total 100% because of rounding. Incident cases not identified under other rubrics. or any coronary disease, differed by age and sex. The ageand sex-specific trends between 1988 and 1998 were similar among the three manifestations of coronary disease (Figure 2), although the incidence of myocardial infarction, myocardial infarction and sudden death combined, and any coronary disease, declined in men and younger persons and remained largely stable or increased in women and older persons. Figure 2. Age- and sex-specific relative risks for myocardial infarction, myocardial infarction and sudden death combined, and any coronary disease (defined in this study as including myocardial infarction, sudden death, angiographically documented disease, and unstable angina) in 1998 versus Horizontal lines denote 95% confidence intervals. DISCUSSION We found that the incidence of hospitalized myocardial infarction and sudden death in Olmsted County declined by 17% between 1979 and 1998, while in the second decade (1988 to 1998), when utilization of angiography had stabilized, trends in myocardial infarction and in myocardial infarction and sudden death combined paralleled coronary disease trends. These findings lead us to consider these two events suitable indicators of trends in coronary disease. We also noted that the incidence of all coronary disease declined modestly by 9% during the second decade, a change that was not statistically significant and not fully commensurate with the decline in coronary disease mortality. Still, myocardial infarction and sudden death did not fully capture the magnitude of the burden of coronary disease in the population, as angiographically diagnosed disease contributed a large and increasing proportion of less severe incident coronary disease cases, thus increasing therapeutic opportunities. Measuring the incidence of coronary disease is challenging. Even though myocardial infarction and sudden death are the most common indicators used to evaluate this incidence, both are explicit and spontaneous events, amenable to diagnostic standardization required for surveillance studies. Changes in the incidence of myocardial infarction during the two decades studied were modest and differed according to age and sex (1,2,12). The present findings on trends in myocardial infarction incidence are consistent with previously reported results August 15, 2004 THE AMERICAN JOURNAL OF MEDICINE Volume

5 from an earlier time period, with a decline in the incidence of myocardial infarction among men and younger subjects contrasting with an increase in incidence among women and older persons (12). Data from Olmsted County and other studies indicate that the incidence of sudden death, defined as an out-ofhospital death due to coronary disease (10), declined less than the incidence of in-hospital deaths (1,2,13,14). The integration of reported trends in myocardial infarction incidence and out-of-hospital coronary disease deaths suggests that the incidence of coronary disease, as measured by these two events, is likely declining (14). However, most studies (1,2,13,14) did not combine myocardial infarction and sudden death as a single incident event and thus provide indirect evidence to that effect. Further, subjects older than 75 years were seldom included; consequently, these reports may not fully reflect trends in coronary disease (1,2,13,14). Our study extends the applicability of observed trends, using a broader set of indicators and no age restriction. Because coronary disease can manifest in ways other than myocardial infarction and sudden death, use of these indicators alone leaves uncertainty with regard to the magnitude of the burden of coronary disease and to the secular trends in incidence. Further, the assumption that myocardial infarction and sudden death reflect incident coronary disease and that trends in these events are linked to primary prevention is likely too simple. These acute events do not account for diagnoses earlier in the natural history of coronary disease, which represent opportunities for secondary prevention and may reduce mortality. Thus, to assess the effectiveness of prevention, it is important to gain insight into other clinical diagnoses of coronary disease and their contribution to trends in incidence. Although new technologies to diagnose coronary disease noninvasively are conceptually suitable for largescale studies, cost and feasibility render their use in population surveillance challenging. Angiography may be used for coronary disease surveillance, as criteria for angiographically diagnosed disease have been standardized. In the present study, angiographic ascertainment led to identification of a larger number of persons with incident coronary disease than did identification using myocardial infarction and sudden death alone. Interpretation of coronary disease trends that incorporate angiographically diagnosed disease requires concomitant consideration of trends in angiography use, which increased in the 1980s (15) and has since stabilized (16). Indeed, the increased use of angiography during the first decade studied could have reduced the time to diagnosis and caused a transient increase in event rates at the beginning of the second decade. Overall, trends in the age-adjusted incidence of coronary disease in the 1990s, measured by combining angiographically diagnosed disease and unstable angina with myocardial infarction and sudden death, paralleled the trends in myocardial infarction and in myocardial infarction and sudden death combined, declining albeit not significantly. Use of angiography continued to increase modestly during the second half of the study period; thus, it is unlikely that the observed decline in coronary disease incidence was confounded by underascertainment of angiographically diagnosed coronary disease. The age- and sex-related differences were remarkably similar for all coronary disease indicators, thereby supporting the robustness of the results. These results also extend previous data on the incidence of myocardial infarction in Olmsted County (12) and indicate a relative shift of the coronary disease burden toward women and older persons. Studies that have relied on myocardial infarction and fatal coronary disease to evaluate the incidence of coronary disease reported little or no secular decline, thereby implying that medical care was the main determinant of the decline in coronary disease mortality. The present study indicates that the incidence of coronary disease, particularly in the second decade, declined modestly when additional indicators were included, although this decline did not fully parallel the concomitant decline in mortality. Thus, secondary prevention may partly explain the decline in mortality. Few surveillance studies have reported on trends in persons aged 74 years or older (1,9). The present findings have implications for primary and secondary prevention in an aging population. The decrease in coronary disease incidence among younger men suggests that primary prevention may be effective among this group while highlighting the need to revisit primary prevention efforts in women and older persons. An increasing proportion of coronary disease cases are identified angiographically, presumably earlier in the course of the disease. This shift in the timing of diagnosis is akin to the phenomenon observed with screening, which can lead to reduction in mortality when early diagnosis provides an opportunity for early intervention (17). Our study has several limitations. The racial and ethnic composition of Olmsted County limits inference to groups not adequately represented in its population. However, no regional population can be representative of the United States as a whole, as illustrated by known regional variations in heart disease rates. The unique strengths of the Olmsted County data reside less in their generalizability than in the ability to examine the determinants of the decrease in coronary disease deaths in a population, because complete longitudinal data are available. The greater occurrence of myocardial infarction and sudden death during the winter months was similar to that reported in the Cardiac Arrhythmia Suppression 232 August 15, 2004 THE AMERICAN JOURNAL OF MEDICINE Volume 117

6 Trial (CAST), a clinical trial with active follow-up (18), suggesting that underascertainment of out-of-area events was unlikely to confound the reported trends. Unstable angina, identified using coded diagnoses, is conceptually subject to shifts in coding practices (19). However, given the relatively small number of cases of unstable angina not identified by the other diagnostic rubrics, changes in coding practices were unlikely to have affected the trends reported. In conclusion, we found that between 1988 and 1998, trends in myocardial infarction and in myocardial infarction and sudden death paralleled overall trends in coronary disease, while the proportion of disease first recognized by angiography increased. Coronary disease incidence, as measured by all indicators, declined modestly, supporting the notion that the decline in coronary disease mortality is multifactorial, explained in part by primary prevention and secondary prevention mediated by earlier detection. REFERENCES 1. McGovern PG, Pankow JS, Shahar E, et al. Recent trends in acute coronary heart disease: mortality, morbidity, medical care, and risk factors. N Engl J Med. 1996;334: Rosamond WD, Chambless LE, Folsom AR, et al. Trends in the incidence of myocardial infarction and in mortality due to coronary heart disease, 1987 to N Engl J Med. 1998;339: Tunstall-Pedoe H, Kuulasmaa K, Amouyel P, et al. Myocardial infarction and coronary deaths in the World Health Organization MONICA Project: registration procedures, event rates, and casefatality rates in 38 populations from 21 countries in four continents. Circulation. 1994;90: Tunstall-Pedoe H, Kuulasmaa K, Mahonen M, et al. Contribution of trends in survival and coronary-event rates to changes in coronary heart disease mortality: 10-year results from 37 WHO MONICA project populations. Monitoring trends and determinants in cardiovascular disease. Lancet. 1999;353: Melton III. LJ History of the Rochester Epidemiology Project. Mayo Clin Proc. 1996;71: U.S. Census Bureau Census Data for Olmsted County, MN. Available at: 7. Roger VL, Jacobsen SJ, Weston SA, et al. Trends in heart disease deaths in Olmsted County, Minnesota, Mayo Clin Proc. 1999;74: Roger VL, Killian J, Henkel M, et al. Coronary disease surveillance in Olmsted County: objectives and methodology. J Clin Epidemiol. 2002;55: White AD, Folsom AR, Chambless LE, et al. Community surveillance of coronary heart disease in the Atherosclerosis Risk in Communities (ARIC) study: methods and initial two years experience. J Clin Epidemiol. 1996;49: Goraya TY, Jacobsen SJ, Belau PG, et al. Validation of death certificate diagnosis of out-of-hospital coronary heart disease deaths in Olmsted County, Minnesota. Mayo Clin Proc. 2000;75: Kennedy JW, Kaiser GC, Fisher LD, et al. Clinical and angiographic predictors of operative mortality from the Collaborative Study in Coronary Artery Surgery (CASS). Circulation. 1981;63: Roger VL, Jacobsen SJ, Weston SA, et al. Trends in the incidence and survival of patients with hospitalized myocardial infarction, Olmsted County, Minnesota, 1979 to Ann Intern Med. 2002; 136: Goraya TY, Jacobsen SJ, Kottke TE, et al. Coronary heart disease death and sudden cardiac death: a 20-year population-based study. Am J Epidemiol. 2003;157: McGovern PG, Jacobs Jr, DR Shahar E, et al. Trends in acute coronary heart disease mortality, morbidity, and medical care from 1985 through 1997: the Minnesota Heart Survey. Circulation. 2001; 104: Weintraub WS, Jones EL, King IIISB, et al. Changing use of coronary angioplasty and coronary bypass surgery in the treatment of chronic coronary artery disease. Am J Cardiol. 1990;65: Krone RJ, Johnson L, Noto T. Five year trends in cardiac catherization: a report from the Registry of the Society for Cardiac Angiography and Interventions. Cathet Cardiovasc Diagn. 1996;39: Morrison AS. Screening. In Rothman KJ, Greenland S, eds. Modern Epidemiology. 2nd ed. Philadelphia, Pennsylvania: Lippincott- Raven Publishers; 1998: Peters RW, Brooks MM, Zoble RG, et al. Chronobiology of acute myocardial infarction: Cardiac Arrhythmia Suppression Trial (CAST) experience. Am J Cardiol. 1996;78: Bertoni AG, Goff DCJ. Declining rate of acute coronary syndrome in the United States, : fact or fiction. Circulation. 2003; 107:e7013. August 15, 2004 THE AMERICAN JOURNAL OF MEDICINE Volume